Electrical signaling system



July 29, 1 947. c. M. THE ILLAUMAS ELECTRICAL SIGNALING SYSTEM Filed April 1, 194a w Mi IN VEN TOR. (Z [ME/VIM 7775/4 Z flUMI-S Arron/v5) Patented July 29, 1947 ELECTRICAL SIGNALING SYSTEM Clement M. Theillaumas, Boulogne Billancourt, France, assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application April 1, 1943, Serial No. 481,508 In France March 29, 1941 4 Claims. 1

The present invention refers to electrical signaling systems and particularly to supervisory means in low frequency signaling systems such as those used in telephone communication, for example.

In low frequency signaling systems supervision is generally very difficult to obtain, particularly when the junction over which the transmission takes place terminates at an operators position.

In order to illustrate these difficulties, and likewise to illustrate the means provided by the present invention for SO1Vil'lg or eliminating them in practice, the case will be considered of signaling by alternating current of a frequency of 50 cycles per second, although the low signaling frequency may be chosen arbitrarily to be of any other suitable value, as employed in the art.

At the two ends, joined by a signaling junction of a system using 50-cycle alternating current, are located the receiving equipments arranged for the signaling, properly speaking, and for the reception of pulses. In the office, on the side of the junction terminating at an operators position the ringing is obtained by means of an alternating current of a low frequency different from that of the signaling, for example 25 cycles per second. This ringing alternating current may be supplied by a special ringing machine at a voltage that may, for example, reach 90 volts. The operator, through the operation of her ringing key, may accidently send ringing current over the junction. Owing to the relatively high voltage of such ringing current, the result thereof may be a lessened efficiency of the system tuned to the signaling frequency passing over the line or else improper operation of the system. In order to simplify the explanation, the signaling current or frequency passing over the line will be called signaling current or frequency and the ringing signaling current or frequency on the operators side will be called ringing current or frequency.

The invention has for one object, to provide means for preventing such accidents as those just described, in low frequency signaling systems.

In the prior art, it has been proposed to overcome these difficulties by inserting between the junction line and the operators position a filter, usually of the high-pass type, designed so as to allow passage of the conversation while barring entry to the operators position of incoming currents of the signaling frequency and also preventing the sending over the line of ringing current of different frequency, which current is to be used only locally.

Experience has shown however that these proposed measures are not sufficiently eflicient to yield a high degree of safety. In fact, if the elements receiving the signaling current are protected well enough, owing to the fact that the signaling current arrives under a low enough potential, for example, 30 volts or even less, the same does not apply to the elements receiving the ringing current because the voltage of the ringing machine at times reaches a high value, 90 volts, for example, as mentioned above. Under these conditions, an outgoing signal may be taken for an incoming signal, or vice versa.

The invention therefore has for another object, to provide means for automatically determining without ambiguity the side of the junction sending the signal, and hence to prevent any wrong interpretation of the signal.

A supervisory system for low frequency signaling according to this invention comprises, in addition to the high-pass filter separating the signaling and ringing pulses of telephone conversations, means for opening the supervisory circuit on the operators side; upon application of a signaling potential to the junction and for opening the same supervisory circuit on the line side when the op erator sends ringing current over the line, while ensuring in both cases a suitable termination of the filter on the open side.

More specifically, a supervisory system incorporating features of the invention comprises, in addition to the high-pass filter separating the signaling and ringing pulses of telephone conversations, a differential two-winding polarized relay, the windings of this latter being traversed respectively by the rectified signaling current and by the rectified ringing current, the armature of this polarized relay serving as a switch for opening, through relays, the supervisory circuit, either on the operators side when signaling it in progress over the line, or on the line side when the operator sends ringing current, terminating resistances being in each case automatically connected into the corresponding end of the filter, by the relays serving to open the supervisory circuit.

The invention is explained in detail in the description that follows, and a schematic embodiment is shown in the accomapnying drawings as one example of an assembly employing this invention.

Referring now to the drawings, the figure shows only that portion of the supervisory circuit and associated elements required for an understanding of the invention. This example of one application cf the invention will be given for the case of low frequency signaling over a telephone line. In that case, the high-pass filter unit indicated as a whole by reference numeral I and inserted in speaking and signaling wires 2-3, may be of any suitable structure for allowing the conversation to pass while strongly damping the signals emitted at low frequency. The out off frequency of this filter I should be higher than 100 cycles per second because certain signals may occur at that frequency but on the other hand it should be lower than 300 cycles per second which is the lower frequency commonly admitted in practice as the limit of the conversation band which must be passed for intelligibility.

On the line side, with respect to filter I, is connected a signaling system sensitive to a low signaling frequency, 50 cycles per second for example. In the figure this signaling system comprises a circuit tuned to 50 cycles per second designated as a Whole by reference numeral 4, and which may consist of a simple resonant circuit or of a tuned primary transformer, a rectifier bridge '5, a telegraph type" polarized relay 6 for the reception of pulses at 50 cycles per second, and the left-hand Winding of a polarized relay 1.

Relay 6 receives the incoming 50-cycle pulses and transmits them to a relay (not shown in the drawing) for controlling suitable recording elements of the system, as may be desired in any particular case.

On the operators side, with respect to filter I, is connected a signaling system sensitive to a low ringing frequency, 25 cycles per second for example. This ringing system comprises a circuit tuned to 25 cycles per second, designated as a whole by reference numeral 8, and which may consist of a simple resonant circuit or of a tuned primary transformer, a rectifier bridge 9, a relay Ill of a type suitable for effecting the ringing operations over the line, and the right-hand winding of polarized relay I.

Relay I receives the 25-cycle pulses sent out by the operator. It controls a relay, (not shown in the drawing) that acts to send over the line at the left-hand side of the drawing, pulses of the same length but at 50 cycles per second.

The 50-cycle signaling pulse circuit passes through the right-hand back contact of a relay I I. Similarly, the 25-cycle ringing circuit passes through the left-hand back contact of a relay I2. These relays each have one armature of the type known in the art as a make before break type, as shown. The operating circuits of these two relays II and I2 pass respectively through contacts I3 and M of polarized relay I whose armature I5 connected to ground is polarized mechanically, or otherwise, in suitable fashion to occupy normally a resting or neutral position that closes neither one of contacts I3 and I4, but leaves both contacts open.

A resistance I6, whose value is determined as later described, is connected between one of the line wires, wire 2 for example, and the left-hand armature of relay II. Another resistance I1, whose value is also described later, is connected between wire 2 and the right-hand armature of relay I2.

The operation of such an arrangement may be explained as follows. When a potential is applied to the junction on the line side, for example (side marked 50 cycles), the left-hand winding of polarized relay I is traversed by a stronger current than the right-hand winding owing to the attenuation introduced by the filter in the line between connection points I8I9 of the circuit of the left-hand winding of relay I and connection points 20-2I of the circuit of the righthand winding. These circuits can be traced for each winding across tuned circuit 4 or 8, the back contact of relay II or I2, a diagonal of rectifier cell 5 or 9, the winding considered, relay 6 or III, the opposite diagonal of rectifier cell 5 or 9 and back to the line.

Since the left-hand winding of relay 1 is traversed by a stronger current than the right-hand winding, and since these windings are arranged so as to have a differential action, armature I5 of relay I will close its left-hand contact I4, thus closing the operating circuit of relay I2 which attracts its armatures and opens its left-hand front contact the supervisory circuit on the operators side (marked 25 cycles), while the ar rangement of the springs of the right-hand make before break contact places resistance I! in loop on the line wires on this side of filter I, in order to provide a suitable termination for this filter.

If, on the contrary, the operator sends 25-cycle current over the line, relay I will bring its armature I5 to close the right-hand contact I3, because the current is, in this instance, stronger in the right-hand winding of this relay. Relay II operates then, and opens its right-hand contact, thus opening the supervisory circuit on the line side and at the same time places, by means of the left-hand make before break contact, resistance I6 in the loop to filter I so as to serve the latter as a terminating resistance. It will thus be seen that the values of resistance I6 and I1 should be chosen so as to provide a suitable termination for the filter on the side where each of them, is at one time or another, placed as a terminating impedance, as Well known in the art.

With such an arrangement, it is evident that interference with the signaling becomes virtually impossible, because the sending side is determined automatically, and that any false signaling or wrong interpretation that might arise from uncertainty as to the side from which a signal comes, is precluded.

What is claimed is:

1. A supervisory system of the character described, including a junction between, an operators and a line section, a high-pass filter located at said junction between said two sections, a polarized relay having two differential windings, first rectifier means feeding rectified signaling current to the first relay winding, second rectifier means feeding rectified ringing current to the second relay winding, secondary relay switching means actuated by said first mentioned relay and so connected as to open the operators side of the supervisory circuit when signaling current passes over the line section and to open the line side of said supervisory system when ringing current is supplied to the operators section of said supervisory system.

2. System according to claim 1, additionally including terminating resistances for said. filter and switching means actuated by said secondary relay switching means so as automatically to connect one of said resistances to the end of the filter connected to the section opened by said relay.

3. A supervisory system for a line junction terminating at an operators position, including a high-pass filter connecting, respectively, the line and operators side of said junction, including on the line side, a circuit tuned to the line signaling frequency and on the operators side a circuit tuned to the operators ringing frequency, two rectifiers connected, respectively, to each tuned circuit, a primary polarized relay having two windings, each connected to one of said rectifiers, said primary relay having an armature normally retained in a neutral and open position, contacts for said armature correspondent to the two positions assumed thereby according to the degree of energization of the respective windings thereof, and secondary relays actuated by the closure of the circuits through said respective contacts of said primary relay, said secondary relays being each provided with an armature acting so as to open the supervisory [circuit on the side of said junction where the current actuating said primary relay does not originate.

4. System according to claim 3 in which said 6 secondary relays are each provided with an additional armature-contact system of the make before brea type, in which two line terminating resistances are provided, each of said armature- 5 contact systems acting to switch the respective side of the line from its normal connection to one of said line terminating resistances.

CLEMENT M. THEILLAUMAS.

10 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 15 Number Name Date 2,036,079 Pullis Mar. 31, 1936 2,004,759 Jester June 11, 1935 1,709,554 Black Apr. 16, 1929 

